Expansion device for use in a working medium circuit and method for operating an expansion device

ABSTRACT

In an expansion device for use in a working medium circuit, for performing a process sequence corresponding to that of a Clausius Rankine cycle or an Organic Rankine cycle, a working unit comprising two interleaved scroll elements is provided of which one is stationary whereas the other is supported for orbiting relative to the stationary scroll element so as to form separate expansion regions between the scrolls moving, upon orbiting of the movable scroll, from the center of the interleaved scroll elements circularly outwardly with increasing volumes in which a working medium admitted at the center can expand for driving the movable scroll element.

This is a Continuation-In-Part application of pending internationalpatent application PCT/EP2011/003764 filed Jul. 27, 2011 and claimingthe priority of German patent application 10 2010 034 230.0 filed Aug,7, 2011.

BACKGROUND OF THE INVENTION

The invention relates to an expansion device for use in a working mediumcircuit in which a working sequence corresponding to a Clausius-Rankinecycle can be carried out. The invention further relates to a method foroperating such an expansion device.

Internal combustion engines today have an efficiency level of up to 40percent. The losses reside predominantly in heat transferred to acooling medium and also in exhaust gas heat.

The prior art resides in various methods and devices, by means of whichelectrical and/or mechanical energy is obtained from the exhaust gasheat and/or the cooling medium heat.

By means of a Clausius Rankine cycle or an Organic Rankine cycle,thermal energy is converted into mechanical energy. An expansion deviceis normally arranged in such a Clausius Rankine cycle performed by axialpiston machine or as a piston expander.

It is the principal object of the present invention to provide animproved, in particular more energy-efficient, expansion device for usein a working medium circuit and an improved method for operating such anexpansion device.

SUMMARY OF THE INVENTION

In an expansion device for use in a working medium circuit, forperforming a process sequence corresponding to that of a ClausiusRankine cycle or an Organic Rankine cycle, a working unit comprising twointerleaved scroll elements is provided of which one is stationarywhereas the other is supported for orbiting relative to the stationaryscroll element so as to form separate expansion regions between thescrolls moving, upon orbiting of the movable scroll, from the center ofthe interleaved scroll elements circularly outwardly with increasingvolumes in which a working medium admitted at the center can expand fordriving the movable scroll element. The expansion ratio of thescroll-type working unit and/or a supply of working media to thescroll-type working unit can be changed.

It is particularly advantageous that by means of the expansion deviceaccording to the invention a rotation movement, for example for drivingan electric generator, can be directly provided.

This rotation movement results in a low-vibration running of theexpansion device, in particular in comparison with an alternatingmovement of a conventional piston expander, wherein the alternatingmovement must additionally be converted into a rotational movement forexample via a gear device.

The expansion device is characterized according to a particularembodiment by a fixed scroll element, a movable scroll element and aneccentric drive, wherein the fixed scroll element comprises a fixedscroll base plate and a fixed scroll spiral wall extending from thefixed scroll base plate, wherein the movable scroll element comprises amovable scroll base plate and a movable scroll spiral wall extendingfrom the movable scroll base plate, and the movable scroll spiral walland the fixed scroll spiral wall are in engagement with each other, sothat they form at least one expansion region between the movable scrollelement and the fixed scroll element. The movable scroll element can bemoved circularly relative to the fixed scroll element by means of theeccentric drive and the size of the expansion region is changed duringthis circular movement along an expansion path. With such an expansiondevice, the number of components is advantageously reduced significantlyin comparison with conventional expansion devices which are formed forexample as an axial piston unit or as a piston expander. In particularthe number of movable components is reduced.

A working medium of the working medium circuit can advantageously becentrally supplied to the expansion device.

According to an embodiment of the invention the working medium flowingin the working medium circuit can be supplied to the expansion device bymeans of a central inlet in the fixed scroll base plate.

According to a further embodiment the working medium of the workingmedium circuit can be supplied to the expansion device by means offurther inlets in the fixed scroll base plate along the expansion path.

According to an advantageous embodiment the working medium of theworking medium circuit can be fed to the expansion device with controland/or regulation by means of at least one cycle valve.

According to an advantageous embodiment a separate cycle valve isassigned to each inlet in the fixed scroll base plate, wherein saidcycle valve can advantageously be separately controlled and/orregulated.

This variable supply of the working medium into the expansion deviceadvantageously results in a variably adjustable pressure level of theworking medium in the expansion device and a variably adjustable workingmedium throughput in the expansion device.

This simple control and/or regulation of the working medium flowfacilitates system design of the working medium circuit.

An expansion pressure gradient within the expansion device is dependentupon the geometry of the scroll spiral walls. This geometry is thuspurposefully adaptable in the design of the expansion device to therespective conditions in the working medium circuit.

The scroll spiral walls are advantageously in the form of Archimedeanspiral surfaces which are arranged displaced angularly by 180° relativeto each other.

It is thus possible with very simple means to vary the working mediumflow in the working medium circuit and/or in the expansion deviceindependently of a pump throughput of a pumping unit arranged in theworking medium circuit.

A pressure difference between a high pressure and a low pressure region,described hereinafter as an expansion gradient, of the working mediumcircuit can advantageously be reduced and/or adapted by means of anincrease in the number of cycle valves arranged along the expansionpath.

Such a reduction results in numerous advantages. For example, through asimultaneous increase in the working medium throughput in the workingmedium circuit, overheating of the working medium can be avoided.

Typically, a low expansion gradient is advantageous in the low engineload range, while a high expansion gradient is desirable in the highengine load range. By means of the expansion device, a particularlyvariable expansion of the working medium can be realized, whereby theworking medium circuit and/or the expansion device is/are flexiblyadaptable to changing heat energy inputs.

During the process for operating an expansion device in a working mediumcircuit, wherein a process sequence is carried out within the workingmedium circuit, which process sequence corresponds to that of a ClausiusRankine cycle or an Organic Rankine cycle, according to the invention amovable scroll element is moved relative to a fixed scroll element bymeans of an eccentric drive in a circular movement so that the size ofan expansion region formed between the movable scroll element and thefixed scroll element is changed during this eccentric drive movementalong an expansion path.

A working medium flow supplied to the expansion device is advantageouslyregulated and/or controlled by means of the separately or jointlyactuated cycle valves.

With this method, a variable expansion of the working medium in theexpansion device is particularly advantageously facilitated.

Therefore, virtually all the heat dissipation energy arising duringoperation of the internal combustion engine can be utilized in theworking medium circuit and in the expansion device, whereby theexpansion device can be adapted to heat dissipation energy quantitiesdiffering depending on the operating state.

As an advantage of the invention, an increase in the degree ofefficiency of the working medium circuit and the expansion device isachieved. By using the heat dissipation of the internal combustionengine, the degree of efficiency of the internal combustion engine isthereby further increased.

The expansion device and the method for operating the expansion devicecan be used particularly advantageously within a given working mediumcircuit operated according to the principle of the Clausius Rankinecycle or the Organic Rankine cycle in order to achieve an optimizedwaste heat utilization of the internal combustion engine.

The invention will become more readily apparent from the followingdescription of an exemplary embodiment thereof with reference to theaccompanying drawings:

Brief Description of Exemplary Embodiments

FIG. 1 shows, schematically, a working medium circuit with expansiondevice,

FIG. 2 shows, schematically, a variant of the expansion device,

FIG. 3 shows, schematically, an alternative variant of the expansiondevice, and

FIG. 4 shows schematically, an illustration of the sequence of theoperatic of the expansion device.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Parts corresponding to each other are provided in all the drawings withthe same reference numerals.

The expansion device 1 is a part of a working medium circuit AK, inwhich a working medium AM is conveyed, and wherein a process sequencecarried out in the working medium circuit AK corresponds to that of aso-called Clausius Rankine cycle or an Organic Rankine cycle, as shownin FIG. 1.

This working medium circuit AK comprises a pumping unit F, a heatexchanger W, the expansion device 1 and a condenser K.

In the process sequence of the Clausius Rankine cycle or the OrganicRankine cycle, the liquid working medium AM is supplied in a workingmedium flow circuit by the pressurizing unit F to the heat exchanger W.In the heat exchanger W, the liquid working medium AM is heated underconstant pressure using the heat dissipation of an internal combustionengine in so that it evaporates.

The heat exchanger W can thereby use—for example as an exhaust gas heatexchanger, exhaust gas recirculation heat exchanger and/or coolingmedium heat exchanger—an exhaust gas heat and/or a heat of a coolingmedium heat of the internal combustion engine in order to heat andevaporate the liquid working medium AM.

The vaporized working medium AM under is fed high pressure to theexpansion device 1 and is expanded in an adiabatic or virtuallyadiabatic expansion to a vapor AM of normal pressure. In the expansiondevice 1, a kinetic energy of the vaporized working medium is therebyconverted into a mechanical energy.

For example the mechanical energy generated can be converted intoelectric energy if the expansion device 1 is coupled with an electricgenerator (not shown in further detail), This electric energy can beused for example to drive an electric motor (not shown in greaterdetail) which supplies additional power to the internal combustionengine. Alternatively, the mechanical energy produced by the expansiondevice 1 could be supplied directly to the internal combustion engine(not shown in greater detail) for the purpose of support.

After expansion, the vaporized working medium AM is fed to the condenserK, in which the vaporized working medium AM is condensed isobarically orvirtually isobarically by cooling and thus converted into a liquidstate, and the liquid working medium AM is returned to the pressurizingunit F on the input side.

FIG. 2 shows schematically an embodiment of the expansion device 1according to the invention.

The expansion device 1 is in the form of a scroll-type working unit,through which the working medium AM flowing in the working mediumcircuit AK can flow in the expansion direction.

The expansion device 1 comprises a fixed scroll element 2 and a movablescroll element 3. The fixed scroll element 2 has a round or disc-formfixed scroll base plate 4 and a fixed scroll spiral wall 5 which extendsfrom the fixed scroll base plate 4 in the direction of the movablescroll element 3. An inlet 6.1 is formed essentially in the middle ofthe fixed scroll base plate 4, for example centrally, for admission ofthe working medium AM from the working medium circuit AK.

The movable scroll element 3 has a round or disc-form movable scrollbase plate 7 and a movable scroll spiral wall 8 which extends from themovable scroll base plate 7 in the direction of the fixed scroll element2.

The scroll spiral walls 5 and 8 are thus formed as so-called Archimedeanspiral surfaces which are arranged angularly displaced by 180°(clockwise) relative to each other.

An expansion ratio within the expansion device 1, which describes apressure difference between a high pressure and a low pressure region ofthe expansion device 1, depends upon the geometry of the scroll spiralwalls 5 and 8. This geometry can thus be purposefully adapted in theconstruction of the expansion device 1 to the respective conditions inthe working medium circuit AK.

The fixed scroll spiral wall 5 is in engagement with the movable scrollspiral wall 8 in such a way that it forms at least one expansion region9.1 between the fixed scroll element 2 and the movable scroll element 3.

In dependence upon the geometry of the scroll spiral walls 5 and 8,further expansion regions 9.2 to 9.5, as shown in FIGS. 3 and 4, can beformed between the fixed scroll element 2 and the movable scroll element3.

These expansion regions 9.1 to 9.4 can be changed in size and move in amanner to be described in further detail circularly along an expansionpath between the scroll spiral walls 5 and 8.

The expansion path is the path defined by each expansion region 9.1 to9.5 during an orbital movement of the movable scroll element 3 relativeto the fixed scroll element 2.

An eccentric drive (not shown) is arranged on the movable scroll baseplate 7, said eccentric drive facilitating on the one hand a orbitalmovement of the movable scroll element 3 relative to the fixed scrollelement 2 and on the other hand supplying a mechanical energy in theform of a rotation movement of a shaft (not shown) connected to theeccentric drive.

The eccentric drive is advantageously formed in such a way that themovable scroll element 3 can be moved relative to the fixed scrollelement 2 along a circle, wherein the movable scroll element 3 does notrotate.

The working medium AM flowing in the working medium circuit AK can befed to the expansion device 1 by means of the inlet 6.1. A conventionalcycle valve is assigned to this inlet 6.1 (not shown in greater detail),said cycle valve facilitating a control and/or regulation of the workingmedium flow which can be supplied to the expansion device 1.

By means of the two outlets 10.1 and 10.2, the expanded working mediumAM can be removed from the expansion device 1. These outlets 10.1 and10.2 are formed periodically, in dependence upon the orbital movement ofthe movable scroll element 3 relative to the fixed scroll element 2, atthe respective outer end 11.1 and 11.2 of the scroll spiral walls 5 and8.

FIG. 3 shows, schematically, an alternative embodiment of the expansiondevice 1 according to the invention.

Besides the inlet 6.1 described in FIG. 1, further inlets 6.2 to 6.5 arearranged in the fixed scroll base plate 4. These inlets 6.2 to 6.5 arearranged along the expansion path in such a way that the expansionregions 9.1 to 9.5 can be accessed during their movement along theexpansion path with working medium AM from the inlets 6.2 to 6.4.

A separate cycle valve is assigned to each inlet 6.1 to 6.5 (not shownin greater detail), By means of these separately or jointly actuatedcycle valves, an individual control and/or regulation of a workingmedium flow which can be fed to the expansion device 1 by means of theinlets 6.1 to 6.5 is facilitated.

FIG. 4 shows, schematically, an illustration of the sequence of theoperation of the expansion device 1.

In order to illustrate the operating behavior of the expansion device 1,FIG. 4 is shows the method steps S1 to S4 in a circular diagram.

In method step S1, the centrally arranged expansion region 9.1 is filledby means of the inlet 6.1 under high pressure from the working mediumcircuit AK. The outlets 10.1 and 10.2 are closed. Further expansionregions 9.2 to 9.5 are formed between the scroll spiral walls 5 and 8along the expansion path.

By the expansion of the working medium AM and the resulting force actingon the scroll spiral walls 5 and 8, the movable scroll spiral wall 8 andthus the movable scroll element 3 are triggered to carry out an orbitalmovement relative to the fixed scroll element.

In the method step S2, this movement circling in clockwise direction isshown following a movement of the expansion regions of 90°. Theexpansion regions 9.1 to 9.3 have enlarged their volume in the process.This results in a pressure and/or temperature reduction of the workingmedium AM, hereinafter described as expansion. The expansion regions 9.4and 9.5 have reached their greatest volume expansion and the outlets10.1 and 10.2 are opened. The expanded working medium AM is fed throughthe outlets 10.1 and 10.2 to the working medium circuit AK and liquefiedin the condenser K.

In the method step S3, the orbital movement of the movable scrollelement 3 is shown after a movement angle of 180°. The expansion regions9.1 to 9.3 enlarge the volume during movement along the expansion path.The outlets 10.1 and 10.2 reach their greatest opening cross-section andthus support a backflow of the working medium AM into the working mediumcircuit AK.

In the method step S4, the orbital movement of the movable scrollelement 3 is shown after a movement angle of 270°. By the orbitalmovement of the movable scroll element 3 relative to the fixed scrollelement 2, a new expansion region 9.1′ has been formed while theexpansion regions 9.1 to 9.3 become larger and continue their movementalong the expansion path in the direction toward the outlets 10.1 and10.2. The outlets 10.1 and 10.2 are virtually completely closed and as aresult the expansion regions 9.4 and 9.5 are eliminated in the furtherprogression of the orbital movement of the movable scroll element 3.

After the completion of a full orbital movement of the movable scrollelement 3 relative to the fixed scroll element 2, the sequence beginsagain in the method step S1.

With the force generated by the pressurized working medium AM and itsexpansion, a shaft (not shown) of the expansion device 1 is driven bymeans of the eccentric drive. An electric generator can thereby bedirectly driven by the expansion device 1.

This rotation movement of the shaft of the expansion device 1advantageously results in a low-vibration running of the expansiondevice 1.

Further inlets 6.2 to 6.5 (not shown in further detail in FIG. 4) can bearranged in the fixed scroll base plate 4 along the expansion path. Byway of these additional inlets 6.2 to 6.5 additional expansion mediummay be supplied to the expansion regions 9.1 to 9.5 during theircirculation in the working medium circuit AL.

A variably adjustable pressure level of the working medium AM in theexpansion device 1 and/or a variably adjustable working mediumthroughput in the expansion device 1 advantageously result(s) from thisvariable introduction of the working medium AM into the expansion device1.

This simple control and/or regulation of the working medium flow AM inthe expansion device 1 advantageously facilitates a system design of theworking medium circuit AK and the control and or regulation of theworking medium circuit AK.

LIST OF REFERENCE NUMERALS

-   1 Expansion device-   2 Fixed scroll element-   3 Movable scroll element-   4 Fixed scroll base plate-   5 Fixed scroll spiral wall-   6.1 to 6.5 Inlet-   7 Movable scroll base plate-   8 Movable scroll spiral wall-   9.1 to 9.5 Expansion region-   9.1′ Expansion region-   10.1, 10.2 Outlet-   11.1, 11.2 End-   AK Working medium circuit-   AM Working medium-   F Pumping unit-   K Condenser-   S1 to S4 Method steps-   W Heat exchanger

1. An expansion device (1) for use in a working medium circuit (AK) forperforming a process sequence within the working medium circuit, saidprocess sequence corresponding to a Clausius Rankine cycle or OrganicRankine cycle, said expansion device (1) comprising a scroll-typeworking unit, through which a working medium (AM) flowing in the workingmedium circuit (AK) is conducted in the expansion direction, with anexpansion ratio of the scroll-type working unit and an adjustable supplyof working medium (AM) delivered to the scroll-type working unit.
 2. Theexpansion device (1) according to claim 1, further comprising a fixedscroll element (2), a movable scroll element (3) and an eccentric drive,with the fixed scroll element (2) having a fixed scroll base plate (4)and a fixed scroll spiral wall (5) extending from the fixed scroll baseplate (4), the movable scroll element (3) comprising a movable scrollbase plate (7) and a scroll spiral wall (8), supported by a crank scrollbase plate (7) so as to be movable therewith, the movable scroll spiralwall (8) and the fixed scroll spiral wall (5) being in engagement witheach other, so that at least one expansion region (9.1 to 9.5) is formedbetween the movable scroll element (3) and the fixed scroll element (2),the movable scroll element (3) moving relative to the fixed scrollelement (2) by means of the eccentric drive, and the size of theexpansion region (9.1 to 9.5) being changeable during the circularmovement of the at least one expansion region (9.1 to 9.5) along anexpansion path.
 3. The expansion device (1) according to claim 1,wherein the working medium (AM) of the working medium circuit (AK) issupplied to the expansion device through an opening formed in the centerof the fixed scroll base plate (4).
 4. The expansion device (1)according to claim 1, wherein the working medium (AM) of the workingmedium circuit (AK) is supplied by way of a central inlet (6.1) in thefixed scroll base plate (4).
 5. The expansion device (1) according toclaim 1, wherein additional working medium (AM) of the working mediumcircuit (AK) is supplied by means of further inlets (6.2 to 6.5) in thefixed scroll base plate (4) along the expansion path.
 6. The expansiondevice (1) according to claim 1, wherein at least one cycle valve isprovided for controlling the supply of the working medium (AM) to theworking medium circuit (AK).
 7. The expansion device (1) according toclaim 6, wherein a separate cycle valve is provided for each inlet (6.1to 6.5) formed in the fixed scroll base plate (4).
 8. The expansiondevice (1) according to claim 1, wherein an expansion pressure gradientwithin the expansion device (1) is dependent upon the geometry of thescroll spiral walls (5 and 8).
 9. The expansion device (1) according toclaim 2, wherein the scroll spiral walls (5 and 8) are in the form ofArchimedean spiral surfaces.
 10. A method for operating an expansiondevice (1) in a working medium circuit (AK), wherein a process sequenceis carried out within the working medium circuit (AK) which correspondsto that of a Clausius Rankine cycle or an Organic Rankine cycle, saidmethod comprising the steps of: moving a movable scroll element (3)relative to a fixed scroll element (2) by means of an eccentric drive ina orbital movement so as to change the size of expansion regions (9.1 to9.5) formed between the movable scroll element (3) and the fixed scrollelement (2) during the orbital movement along an expansion path formedbetween the scroll elements (2, 3).